The technical field of this invention is the detection of a loose or detached electrical circuit module.
Electrical circuit modules containing accelerometers are generally adapted for mounting in a fixed relationship with some product or device. An example is a control module adapted for mounting on a vehicle seat pan, such as an occupant detection module used in a passive restraint deployment control. Such detection modules may incorporate an accelerometer mounted therein, for example on an electric circuit board, and providing an acceleration signal to a circuit on the board. But if the module becomes loose or detached from the seat pan, or the circuit board becomes loose or detached from the module, the accelerometer will no longer accurately sense and signal the accelerations of the seat pan (or other device) to which it is supposed to be fixed.
This invention is an electric circuit module adapted for attachment in a mounted position to a vehicle part comprising a magnetic material. The module has a case made of a non-magnetic material and having an attachment portion and a permanent magnet fixed within the case. The module further has a Hall effect sensor fixed within the case in positional relation to the permanent magnet and the attachment portion such that the Hall effect sensor generates a first signal when the attachment portion of the case is fixedly attached to the vehicle part comprising a magnetic material and a second signal different from the first signal when the attachment portion of the case is not so mounted. The module also has an electric circuit in the case with circuit elements responsive to the Hall effect sensor to provide a first mode of operation in response to the first signal and a second mode of operation in response to the second signal. The module is particularly useful when at least one of the electric circuit elements is an accelerometer, for example in a vehicle passive restraint deployment system. In such an application, the accelerometer is fixedly attached to a vehicle body part to indicate the acceleration thereof. Typically, the vehicle body part is made of a magnetic material; and the system will respond to the first signal from the Hall effect sensor, which indicates that the accelerometer is fixedly attached to the vehicle body part, by declaring the accelerometer output signal as valid but will respond to the second signal from the Hall effect sensor, which indicates that the accelerometer is not fixedly attached to the vehicle body part, by declaring the accelerometer output signal as invalid.